Since the beginning of CT, cardiac imaging has been a key technology driver. Multiple innovations have attempted to address the associated need for high temporal resolution. Although current CT systems can image a cross-section of the heart in about 100 milliseconds or less, this may not be sufficiently fast for obtaining full diagnostic information. This is particularly the case when imaging uncooperative patients or patients with arrhythmia.
Organ, body, or object speed of coverage in CT is achieved through a combination of effective source rotation speed and longitudinal (or “z”) —extent of the detector. Source rotation angular velocity is limited by the flux requirement and the capability of source sub-systems to withstand the large rotation-related accelerations.
In the mid-1980s, electron beam tomography (EBT) was developed as a means to acquire projection data for one or up to four tomographic slices in about 50 milliseconds. The technology circumvented the mechanical difficulties associated with the accelerations above mentioned, but did not provide a high enough X-ray beam flux to enable high contrast-to-noise imaging and also suffered from a number of additional technological limitations, such as the requirement for an intrinsic cone-angle in the acquisition data—that is, the central detector plane and the X-ray source rotation plane are necessarily offset along the main system axis (“z”).
CT systems with a rotating gantry typically have only one radiation source; although at least one medical imaging system is commercially available with two radiation sources, leading to a factor two temporal resolution increase in specific applications, such as cardiac imaging. In that system, the X-ray projections from the two sources do not overlap on the detector side, and, due to space constraints on the rotating gantry, the imaging field-of-view exposed by both sources is limited as compared to single-source CT.
Rotating anode tube designs have adapted to the requirement for higher flux by providing larger diameter anodes and higher anode rotation speeds. These anode diameter increases however only compound the mechanical challenges associated with high angular velocities around the imaging field-of-view (FOV).
Certain CT aviation security systems use multiple sources arranged on a fixed gantry. With today's X-ray tube technology, this necessarily results in a relatively sparse sampling in the view-angle (projection-angle) direction.